ISO 3146 Plastics - Determination of the Melting Behavior (Melting Temperature or Melting Range) of Semi-Crystalline Polymers by Capillary Tube and Polarizing Microscope Methods

The ISO 3146 Plastics - Determination of the melting behavior (melting temperature or melting range) of semi-crystalline polymers by capillary tube and polarized microscopy methods standard, published by the International Organization for Standardization (ISO) , describes two test methods for evaluating the melting behavior of semi-crystalline polymers:

• Method A Capillary tube: This method is based on changes in the shape of the polymer. It is applicable to all semi-crystalline polymers and their compounds. This method is also considered useful in evaluating the softening of non-crystalline solids.
• Method B Polarizing microscope: This method is based on changes in the optical properties of the polymer. It is applicable to polymers containing a birefringent crystalline phase. However, it is not considered suitable for plastic compounds containing pigments or other additives that may interfere with the birefringence of the polymeric crystalline phase. Another method applicable to semi-crystalline polymers is described in ISO 11357-3 Plastics - Differential scanning calorimetry (DSC) - Part 3: Determination of temperature and enthalpy of melting and crystallization.

For the purposes of this standard, the terms and definitions given in ISO 472 apply. In addition, the melting range refers to the temperature range at which crystalline or semi-crystalline polymers lose their crystalline properties or particle shape when heated. The melting temperatures determined in methods A and B are included in this standard.

Method A In the capillary tube test method, in principle, a test sample is heated at a controlled rate and the temperature of the sample is measured at the first visible change in shape and again at the moment when the last traces of the crystalline phase have disappeared. The first temperature is taken as the melting temperature of the sample, while the interval between the two temperatures defines the melting range. This method may be used for non-crystalline materials when deemed necessary by the relevant specifications or by agreement between the parties concerned.

The equipment used in these tests includes:

• Melting device. This equipment consists of the following items:
  • A cylindrical metal block with a hollow top, forming a chamber.
  • Metal plug with two or more holes that allow a thermometer and one or more capillary tubes to be mounted in the metal block.
  • Heating system for metal block equipped with a suitable temperature controller
  • Four heat-resistant glass windows arranged diagonally at right angles to each other on the side walls of the chamber. A lens is placed in front of one of these windows to observe the capillary tube. The other three windows are used to illuminate the interior of the chamber by means of lamps.

In the meantime, other suitable types of melting devices may be used provided they give the same results.

• Capillary tube made of heat-resistant glass, closed at one end. Maximum outer diameter should preferably be 1,8 mm.
• Calibrated thermometer graduated in 0,1 degree divisions. The thermometer bulb must be positioned so that heat dissipation in the device is not hindered. Other suitable temperature measuring devices may also be used.

The test samples used in principle should be representative of the material to be tested. Powder with a particle size of up to 100 µm or cut film pieces with a thickness of 10 µm to 20 µm should preferably be used. Comparison tests shall be carried out on test samples with the same or similar particle size or, in the case of layers or films, on test samples of similar thickness. Unless otherwise specified or agreed upon between the parties concerned, the test sample shall be conditioned for 291 hours at a temperature of 3 degrees plus/minus 23 degrees and a relative humidity of 2 percent plus/minus 50 percent in accordance with ISO 5 before measurement.

Meanwhile, the thermometer should be calibrated periodically with reagent grade or certified chemicals in the temperature range used for the test. Recommended chemicals for calibration purposes are included in the table provided in the standard.

Among the numerous testing, measurement, analysis and evaluation studies that our organization has provided for businesses in various sectors, our organization also provides testing services defined in the standard “ISO 3146 Plastics - Determination of melting behavior (melting temperature or melting range) of semi-crystalline polymers by capillary tube and polarized microscope methods” with its trained and expert staff and advanced technological equipment.